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Drinking Water Contaminants Research

Today, our nation's drinking water supply is one of the cleanest in the world. Even so, microbes, chemicals, and pathogens are still a concern. EPA has set standards for about 90 contaminants that can affect drinking water.


Microbes are tiny organisms that can cause diseases. Waterborne diseases killed thousands of people around the world before water treatment was developed. Microbes that cause waterborne diseases include:

  • bacteria, which can cause cholera and typhoid;
  • viruses, which can cause polio, hepatitis, and various gastrointestinal diseases; and
  • protozoa, which can cause giardiasis and cryptosporidiosis.

EPA is pursuing several research areas that address microbes in drinking water:

  • Microbial source tracking, identifying fecal pollution sources
  • Wastewater biosolids, residuals from wastewater treatment
  • Techniques to detect and remove or disable microbial contaminants
  • Methods of disinfection

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EPA’s research on chemical contaminants focuses on:

  • sources of endocrine disrupting chemicals (EDCs), chemicals with the potential to interfere with natural hormones in the body responsible for the maintenance of homeostasis and the regulation of developmental processes
  • the risks of  using of pesticides,
  • the effect of personal care products on our drinking water, and
  • comparing the risks from microbial pathogens in our drinking water against the risks of creating disinfection by-products.

Scientists are also looking at emerging chemical contaminants. They may be currently unregulated. They occur at low levels, enter the water from multiple sources. These chemicals are considered a long-term issue (not an issue that requires emergency action). Some of these chemicals may have harmful effects on both wildlife and humans.

Monitoring for specific contaminants is conducted at selected drinking water utilities. Chemical analyses are performed by the utilities or by commercial laboratories. EPA determines the amount and the risk posed to the public. EPA will take appropriate action for that chemical contaminant - either regulation, guidance, or a decision not to regulate.

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Pathogens are small life forms that can cause disease. Pathogens are microorganisms, such as

  • bacteria,
  • fungi,
  • protozoa, and
  • viruses.

They’re often found in water as a result of

  • sewage discharges that contain fecal matter,
  • leaking septic tanks, and
  • runoff from animal feedlots.

One microorganism of concern is Cryptosporidium. This protozoan parasite enters our source water through sewage and animal waste. It causes cryptosporidiosis, a mild gastrointestinal disease. EPA requires at least 99 percent of Cryptosporidium protozoa be removed by filtered surface water systems serving 10,000 people or more.

Giardia lamblia, another troublesome pathogen, also infects the gastrointestinal tract. It causes giardiasis. Waterborne giardiasis may occur as a result of disinfection problems or inadequate filtration procedures. EPA requires water systems to disinfect or filter their water so that 99.9 percent of Giardia is physically removed or rendered harmless.

Small water distribution systems face unique challenges when it comes to protecting drinking water from Cryptosporidium and Giardia lamblia. So EPA’s investigates the risk trade-offs with disinfection by-products and ways for small systems to control microbial pathogens.

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